7.4 Warm-Up: Area Review

7.4 Warm-Up: Area Review

Review the area of 2D figures

Area of a Rectangle

•  $A=bh\ \ \ or\ \ \ \ A=lw$  

• Area of a rectangle equals the base times the height, or...

• Area of a rectangle equals the length times the width

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Area of a Triangle

•  $A=\frac{1}{2}bh$  

• Area of a triangle is half of the base of the triangle times the height of the triangle (base of the triangle times the height of the triangle, divided by 2)

• REMEMBER: the base is always a side, and the height is always a right angle to the base

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Area of a Circle

•  $A=\pi r^2$  

• Area of a circle equals 3.14 times the radius, times the radius again

• REMEMBER: radius is halfway across the circle

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Multiple Choice

What is the area of the half circle with a diameter of 8 (radius of 4)?
(hint: calculate the area of the whole circle, then divide by 2 to find half of it)

•  $50.24\ cm^2$   
  

•  $12.56\ cm^2$  
  

Compound Area

• Area of a compound figure can be found by:

• 1) identify the shapes in the compound figure

• 2) calculate the area of each shape

• 3) add the areas together

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